Considering we just had our last Splatfest, I would not be suprised if Splatoon 3 gets announced next year TBH. That could cut the legs off of Splatoon 2, and considering how 2 was released at the start of this gen, it would not be far fetched to think a 3rd game could land on the same hardware.
That is the only scenario where I see this prediction not being at least close to being true.